[libre-riscv-dev] Change pspec to class hierarchy

[Jacob Lifshay]

Any objections to my (or someone else) changing pspec (pipeline spec?)
to a class hierarchy?

My reasoning is that extensive documentation can then be attached to
the class definitions instead of not having a good location for the
documentation as well as being able to just use pspec.width instead of
pspec['width'] (for example), which allows for better auto-completion.
changing to a class hierarchy also gives pspec more structure, which
benefits readability.

Jacob